feat(shell-docs): add IframeSwitcher component for demo+code tabs

Several MDX files import `IframeSwitcher` from `@/components/content`
(prebuilt-components, frontend-tools, interactive, tool-rendering, plus
integration overrides), but the component file was missing. This adds it
as a thin wrapper around the existing `<Tabs>` component, rendering a
demo iframe and a code iframe in a Tabs strip.

Props: `exampleUrl`, `codeUrl`, `exampleLabel` (default "Demo"),
`codeLabel` (default "Code"), `height` (default "600px"). Both iframes
are sandboxed and lazy-loaded.

Matches the upstream IframeSwitcher pattern used on docs.copilotkit.ai
to render embedded feature-viewer demos alongside their backing code.

Author: samjulien

showcase/shell-docs/src/components/content/iframe-switcher.tsx

@@ -0,0 +1,49 @@
+"use client";
+
+import { Tabs, Tab } from "../docs-tabs";
+
+interface IframeSwitcherProps {
+  id?: string;
+  exampleUrl: string;
+  codeUrl: string;
+  exampleLabel?: string;
+  codeLabel?: string;
+  height?: string;
+}
+
+export function IframeSwitcher({
+  exampleUrl,
+  codeUrl,
+  exampleLabel = "Demo",
+  codeLabel = "Code",
+  height = "600px",
+}: IframeSwitcherProps) {
+  const iframeStyle = {
+    width: "100%",
+    height,
+    border: "none",
+    borderRadius: "0.375rem",
+    background: "var(--bg-surface)",
+  };
+
+  return (
+    <Tabs items={[exampleLabel, codeLabel]}>
+      <Tab value={exampleLabel}>
+        <iframe
+          src={exampleUrl}
+          style={iframeStyle}
+          sandbox="allow-scripts allow-same-origin allow-forms allow-popups"
+          loading="lazy"
+        />
+      </Tab>
+      <Tab value={codeLabel}>
+        <iframe
+          src={codeUrl}
+          style={iframeStyle}
+          sandbox="allow-scripts allow-same-origin allow-forms allow-popups"
+          loading="lazy"
+        />
+      </Tab>
+    </Tabs>
+  );
+}

showcase/shell-docs/src/components/content/index.ts

@@ -0,0 +1 @@
+export { IframeSwitcher } from "./iframe-switcher";